Liquid-phase Controlled Synthesis Of Vanadate-based Nanomaterials And Study On Their Electrochemical Properties

Transition metal vanadates(TMVs)have a variety of oxidation states from V²⁺to V⁵⁺,as well as inherent synergies between a variety of metals,which can provide a rich crystal structure and redox reactions,while vanadium oxides have high theoretical capacity and excellent electrochemical properties as both lithium-ion battery anode materials and zinc ion cathode materials,and in recent years have attracted domestic and international attention as a new class of electrode materials.As a new class of electrode materials,TMVs have attracted a lot of attention from researchers at home and abroad.However,TMVs have the following major problems:(1)due to their variable valence properties,it is difficult to obtain pure phase products due to the mixing of multiple valence impurities in the synthesis process;(2)the conductivity and cycling stability of the electrode are limited due to structural instability and rapid volume changes during charging and discharging;(3)when used as the cathode for zinc ion batteries,the charge repulsion between Zn ions and transition metal ions leads to the formation of Zn ions.The charge repulsion between Zn²⁺and transition metal ions leads to slow diffusion of Zn²⁺into the TMVs material lattice in the solid state.To address the above problems,this thesis presents the controlled synthesis of pure phase zinc vanadate(Zn₃(VO₄)₂)and hydrated zinc vanadate(Zn_0.15V₂O₅·0.2H₂O)by liquid phase method for lithium ion battery anode and aqueous zinc ion battery cathode,respectively,through the regulation of Zn₃(VO₄)₂morphology for lithium ion battery anode and Zn_0.15V₂O₅·0.2H₂O intercalation of zinc ions and crystalline water for zinc ion battery cathode.to effectively solve the above problems and further investigate the mechanism.Specifically,the following two parts of work were included:(1)Pure-phase two-dimensional layered Zn₃(VO₄)₂ porous nanosheets formed by cross-linking of monolayer nanoparticles were prepared by a simple co-precipitation and calcination method.The electrochemical performance of Zn₃(VO₄)₂ as an anode for Li-ion batteries was investigated.The reversible discharge capacity of the Zn₃(VO₄)₂porous nanosheets was 773 m Ah g^-1 at a current density of 1.0 A g^-1,with a capacity retention rate of 94%after 700 cycles.Furthermore,a reversible discharge capacity of445 m Ah g^-1 can be maintained after 1200 cycles at a current density of 5 A g^-1.Even at higher current densities of 10.0 A g^-1,a high reversible capacity of 527 m Ah g^-1 can be achieved,maintaining a capacity of 163 m Ah g^-1 after 1200 cycles.(2)A simple hydrothermal method is proposed for the preparation of Zn_0.15V₂O₅·0.2H₂O porous microspheres.As a rechargeable aqueous zinc ion battery cathode material,the electrochemical properties of zinc ion intercalated water and vanadate microspheres were investigated.At a current density of 0.1 A g^-1,the Zn_0.15V₂O₅·0.2H₂O microspheres have a reversible discharge capacity of up to 410 m Ah g^-1.At a current density of 5 A g^-1,a reversible discharge capacity of up to 310 m Ah g^-1can be maintained at 210 m Ah g^-1 after 5000 charge/discharge cycles.even at a high current density of 10.0 A g^-1,a high reversible capacity of up to 243 m Ah g^-1 can be provided,which is maintained at 197 m Ah g^-1 after 10000 cycles,with a capacity retention rate of more than 81%.The electrochemical properties of the material were investigated on the basis of the intercalated metal ions and crystalline water on the electrochemical properties and the diffusion rate of Zn²⁺,the optimum ratio of which is a key factor affecting the electrochemical properties.